The composition and process of preparing polymer blends from a water-dispersible or dissipatable polyester and an acrylic polymer are disclosed in an application of Mahendra K. Sharma filed even date herewith entitled "Process for Preparing Blends of Polyesters and Acrylic Polymers", incorporated herein by reference in its entirety. It has been demonstrated that such polymer blends exhibit certain improved properties as compared to use of polyester alone. Prior art of interest includes U.S. Pat. Nos. 4,704,309; 4,738,785; 4,883,714 and 4,847,316 which relate to aqueous ink compositions containing water-dispersible polyesters. U.S. Pat. No. 4,623,680 teaches a method of preparing polymer blends from ammonium or amine salt of a carboxyl functional acrylic copolymer mixed with phenolplast resins useful as a can coating composition. The polyepoxide resins are partially reacted with a monofunctional acid group and, optionally, an epoxidized hydrocarbon or vegetable oil.
U.S. Pat. No. 4,395,500 by Gernot and Rolf discloses a method of preparing polymer blend of styrene and esters of acrylic or methacrylic acid. The aqueous resin solution provides a bimodal particle size distribution with 10 weight % of particles having an average diameter of less than 0.2 .mu.m and of 90 weight % of particles having an average diameter of more than 0.25 .mu.m. The ratio of average grain size of coarse to fine polymer is at least 2:1. These resin dispersions are claimed to be suitable especially as binders in plasters and gloss paints.
U.S. patent application No. 225,520 relates to an ink composition containing a blend of a polyester and an acrylic polymer. It was observed that the water-dispersible polyester material, when mixed with an acrylic polymer, can provide good water resistance and good block resistance without sacrifice of the advantages of water-dispersible polyester alone. This polymer blend was used to formulate water-based inks, overprints, and ink primers.
U.S. Pat. No. 4,921,899 discloses an ink composition containing a blend of a polyester, an acrylic polymer and a vinyl polymer. The water-based inks containing the blend of these polymers as a binder can significantly improve ink film properties such as alcohol resistance, block resistance and water resistance as compared to use of water-dispersible polyester alone. The polymer blends were also employed to prepare ink primers and overprint varnishes. However, these polymer blends were prepared by mixing an aqueous polyester dispersion with an acrylic emulsion which contains surfactants and other additives. The presence of surfactants in the ink formulations creates several problems related to ink stability, printing process and print quality of the ink film.
The previous work as described above relates to the composition of polymer blends, process of preparing these blends and their use in the formulation of water-based inks. The use of aqueous polymer blends containing a polyester and an acrylic polymer in pigment grinding is disclosed in the present invention. These pigment millbases and formulated water-based inks exhibit many desirable properties such as superior adhesion, wetting of printed substrates, flow-out, lay, scuff resistance, water-resistance, gloss and blocking temperature.